1. Field of the Invention
The invention relates to a reactor for coating flat substrates as well as to a process for manufacturing flat substrates using reactors of the above-mentioned type.
2. Description of the Related Art
Reactors for coating substrates using CVD-processes and particularly MOCVD-processes as well as plasma coating processes require a reaction gas flow through the so-called reactor vessel or reaction vessel in which the substrate(s) to be coated is/are arranged. In order to achieve an excellent coating of the surface of the substrates, it is required to guide the reaction gas flow as uniformly as possible, that is, in a laminar flow so closely past the substrate surface that a layer formation takes place on the substrate which is as homogeneous as possible.
During the manufacturing of "normal" layers, high temperatures are, however, required during the coating process which, among others, have heat convection effects within the gas flow and thus lead to a disturbance of the laminar flow. Although it is possible to increase the laminarity and thus the parallelism of the reaction gas flow relative to the coating surface by means of an increased reaction gas flow rate, transversal flow components may also occur within the reaction vessel caused by convection but also by constructive obstacles which stand in the way of the reaction gas flow. Within the reactor vessel, such transversal flow components lead to the formation of local vortexes which have a negative influence on the coating process.
On the basis of the occurring turbulent flow regions, it can also be explained that the layer formation on the preferably flatly designed substrate does not take place uniformly but that points occur which have a higher layer depositing as well as points which have a lower layer depositing.
In addition, in the case of the known reactor systems, in which the substrates to be coated are arranged on the bottom of the reaction vessel, surface effects occur which are the result of condensate deposits which form on the reactor walls during the coating process and, dependent on the amount of condensate, fall downward from the upper reactor walls and damage the surface of the substrate.